In vehicles, in particular in road vehicles, a need exists to supply a vehicle interior, preferably a passenger compartment, with clean air. The supplying of the vehicle interior with air usually takes place by means of an air conditioning system which draws in air from the interior, cleans it by means of an interior air filter, and returns it to the interior (recirculating air operation), or draws in fresh air from the environment and cleans it by means of the interior air filter and delivers it to the interior (fresh air operation). Likewise, in modern air conditioning systems any intermediate positions between such a recirculating air operation and such a fresh air operation are possible (mixed air operation). Whereas such an interior air filter originally only had to filter out coarse impurities from the air, the demands on such interior air filters and the filter materials coming into use here have increased constantly. In the meantime, by means of an interior air filter, a cleaning of the drawn-in air of pollen, fine dust and odours is to be achieved. In particular, the removal of odorous substances from the drawn-in air presents difficulties here, because different odorous substances also require different filter materials. If, however, for an increasing number of different odorous substances a corresponding number of different filter materials becomes necessary, the throughflow resistance of the air filter increases, which prevents an economical mode of operation of the air conditioning system. Therefore, multilayer filter materials preferably come into use, which always represent an optimized compromise for the respective cleaning task. In so far as such an air filter can filter out both particulate impurities, therefore solid and/or liquid impurities, and also gaseous impurities from the air, such an air filter is frequently also designated as a hybrid filter. Such hybrid filters are readily itemized via specifications which generally take the following gases into consideration: n-butane, toluene, sulphur dioxide, nitrogen oxides, ozone. These hybrid filters are specified for example according to ISO Standard 11155 Part 2. However, this standard specification represents odour pollutions which were identified in European areas of high population density approximately 30 years ago. Present-day external air conditions, such as are present in the areas of high population density in Europe and especially in Asia differ, however, from these earlier external air conditions. For example, the ambient air today can contain amines and aldehydes which transport odours and which can not, or can only be insufficiently filtered by the above-mentioned hybrid filters according to standard specification.
From DE 10 2005 016 677 A1 a filter element with a multilayer filter material is known, in which an active layer arranged on the inflow side is provided with active carbon fibres, to which an adsorber layer with granular adsorbents adjoins on the outflow side. A further active layer with active carbon fibres can adjoin this adsorber layer on the outflow side. The adsorbents which are used here can comprise active carbon, zeolites, cyclodextrins, silicates, ion exchangers and aluminosilicates.
From DE 10 2012 007 503 A1 another adsorptive filter medium is known, in which a plurality of first filter layers are provided with a first adsorption substance and a plurality of second filter layers, different from the first filter layers, are provided with a second adsorption substance, which alternate and have different throughflow resistances or respectively pressure losses.
A further adsorptive filter material is known from DE 10 2009 021 020 A1 and contains an exchange resin which is loaded with metal cations.
A further difficulty which can occur in filters of a vehicle air conditioning system is the accumulation and multiplication or respectively growth of microorganisms, such as e.g. bacteria, algae and fungi, on the filter material. These microorganisms can arrive into the passenger compartment from the air stream, so that ultimately the passengers are exposed to these microorganisms.